A feature of the present invention is to provide dual modulus oriented elastomeric filaments to be used in a seat suspension element in a vehicle seat assembly that is a block copolymer material capable of being oriented to provide a two-stage modulus in the direction of the suspension span for providing a high comfort index under static load support conditions and an increasing load support characteristic for absorbing road impacts.
Traditionally, molded foam cushioning elements of the type set forth in U.S. Pat. No. 3,161,436 have been used in automobile and vehicular applications to provide a vehicle seating assembly with both static and dynamic load supporting characteristics for passenger comfort. In such applications, the element is supported by a rigid backing member forming part of the seat assembly frame for attachment to the vehicle body. The modulus of elasticity of the foam cushioning element and the thickness of the element is selected to provide a static deformation which conforms to and comfortably supports the weight and shape of the different passengers.
The cushioning elements have a modulus and are dimensioned to absorb dynamic impacts which are transferred through the vehicle suspension system into the seat assembly. In such cases, the modulus and dimensions of the seating element are selected to absorb the impact loading without causing the foam element to fully compress and bottom out against the rigid backing member.
Such objectives can only be combined by use of foam elements having a thickness that will produce impact load absorption in a material of a modulus that has a comfortable feel under static load conditions. Such thickness of the foam element increases the weight of the vehicle seat assembly.
U.S. Pat. Nos. 2,251,318 and 4,545,614 disclose vehicle seat assemblies in which elastomeric webbing or strips are stretched between vehicle seat frame components to form a suspension for a seat cover. In the case of the '318 patent, the strips are covered by a layer of foam material like sponge material which will impart static comfort to the assembly. The strap components are configured to yield to accommodate impact loads. The straps are reinforced by fabric to control against excessive deflection of natural rubber material of the straps.
The '614 patent uses strips or fibers of a material having a modulus at high deformation which is a multiple of natural rubber to control bottoming out of the suspension system. The use of strips, filaments or straps requires a cover to impart a smooth seating surface. Such covers can set to the shape of the underlying strip array following periods of use.
Orientation of various polymeric materials is performed to achieve improved properties such tensile strength, creep resistance, abrasion, and permeability resistance. These various polymers include crystalline thermoplastics, non-crystalline thermoplastics, thermoplastic elastomers, and conventional cross-linkable elastomers. However, none of these commercially available materials in a filament form can be used in a seat suspension application. Some commercial filaments are highly elastic and are excellent for comfort but provide poor support due to their low modulus values. Other filaments have very high modulus values and provide excellent support but are poor on comfort.
It is therefore an object of the present invention to provide a fairly flexible elastomeric filament to provide comfort in a seat suspension and allow an appreciable reduction of the foam material currently used in seat suspensions.
It is another object of the present invention to provide an oriented elastomeric filament for seat suspension applications that has a good balance of physical properties of elastic behavior and high modulus.
It is yet another object of the present invention to provide an oriented elastomeric filament that is tensioned during extrusion to orient the molecular structure of the material and then annealed to fix the material orientation for establishing a two-stage modulus characteristic in the filament.
It is still another object of the present invention to provide an oriented elastomeric filament for absorbing vehicular vibrations and providing increased support in response to increased load.